att.net account no longer works at yahoo - Sorry, we don't recognize this email.

I got gigapower installed back in April.   I had a working att.net email account setup at the time. 

At some point in the past month that account stopped working at the yahoo end.  I can login fine at att.net and click the 'Mail' link that takes me to yahoo.

At this point if I enter the same att.net email it says 'Sorry, we don't recongnize this email'.

I tried using the chat support to fix this and then I got a call from a represenative.  At the end of the call the person told me to call yahoo.

I don't see any way for me to contact yahoo about a email account that is suppose to be tied to my att.net login.